Milling wheels for small flour mills

ABSTRACT

A matched pair of coaxial milling wheels for small flour mills such as those used in homes. A stationary milling wheel and an adjacent rotatable milling wheel each have a common central axis. Each includes first and second radial surfaces spaced along the axis. The adjacent faces of the wheels have a center cavity extending axially inward and defining the inner periphery of an annular milling face extending to the wheel periphery. Complementary grooves are formed in the milling face of both wheels to feed grain radially outward from the central cavities and to assist in cracking and grinding the particles to a fine state. The wheels are formed integrally from fired stoneware and have machined flat annular rims about the milling faces to assure accurate final grinding of the particles before they exit from the space between the two wheels.

BACKGROUND OF THE INVENTION

This disclosure relates to milling wheels of the type used in home grainmills having a stationary milling wheel and an adjacent powered orrotatable milling wheel. Examples of these types of mills are shown inthe Kuest U.S. Pat. No. 3,688,996 and the Grover U.S. Pat. No.3,880,367. Another description of grain milling wheels is contained inU. S. Pat. No. 3,942,730 to Coucher. A further disclosure and discussionof this type of mill is set out in my co-pending application Ser No.680,490 filed Apr. 26, 1976, now U.S. Pat. No. 4,039,153, issued Aug. 2,1977, which is hereby incorporated by reference.

Experience in milling grains by use of home mills has been erratic. Mostsuch mills utilize very hard abrasive grinding or milling wheels whichare relatively expensive and are easily clogged by the material beingground. Furthermore, the use of very hard abrasive surfaces in closeproximity to one another while rotating at a high speed pose seriousproblems of surface damage if the surfaces are brought into contactaccidently. It has also been difficult to attain the degree of finemilling needed to produce cake flours from wheat, and virtuallyimpossible to mill oily materials, such as corn or soft oily materialssuch as soybeans.

SUMMARY OF THE INVENTION

The matched pair of coaxial milling wheels for small flour mills includea stationary milling wheel fixed relative to a central axis and acoaxial rotating milling wheel powered about the central axis. Themilling wheels each have first and second axially spaced radialsurfaces. A center cavity extends axially inward from the first radialsurface of each wheel. An annular milling face is located about thefirst radial surface between the center cavity and the periphery of thewheel. The milling face has a plurality of grooves angularly spacedabout the central axis of the wheel. Each groove extends from the centercavity to a location spaced inwardly from the milling wheel periphery,thereby defining an outer annular rim about the edges of the millingface. The grooves on the respective milling wheels are designed tofacilitate cracking and feeding of granular material as it moves fromthe center cavities of the wheels to the annular rims. The surfaceconfigurations on the two complementary rims are such as to make maximumuse of the rotational movement between the two wheels to facilitatecracking and grinding of the grain particles.

It is a first object of this invention to provide a pair of practicalmilling wheels which can be fabricated from relatively inexpensivematerials, such as fired stoneware. The resulting milling wheels aredurable and can be replaced, when eventually worn, at a relativelymodest cost in comparison to wheels constructed of hard abrasivematerials.

Another object of the invention is to provide milling wheels which haverelatively smooth surface configurations in comparison to the surfacesof harder abrasive materials, and which therefore are not subject tobeing clogged by the material being milled. The present wheels areessentially self-cleaning in use, and can be readily brushed clean orwashed when necessary.

Another object of this invention is to provide a set of milling wheelswhich can be fabricated to precision tolerances to permit exceptionallyfine milling of flour in a home grain mill.

These and further objects will be evident from the following disclosureand the accompanying drawings which illustrate a preferred embodiment ofthe milling wheels.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified fragmentary sectional view through a verticalplane within a grain mill, illustrating use of the milling wheels;

FIG. 2 is a plan view of the operative face of the stationary millingwheel;

FIG. 3 is a sectional view taken along line 3--3 in FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view taken along line 4--4in FIG. 2;

FIG. 5 is an enlarged fragmentary sectional view taken along line 5--5in FIG. 2;

FIG. 6 is a plan view showing the operative face of the rotatablemilling wheels;

FIG. 7 is a sectional view taken along line 7--7 in FIG. 6;

FIG. 8 is an enlarged sectional view taken along line 8--8 in FIG. 6;and

FIG. 9 is an enlarged fragmentary view taken along line 9--9 in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

This disclosure relates to a matched set of milling wheels for home use.The milling wheels are capable of being used in various poweredarrangements, FIG. 1 merely illustrating a basic mounting arrangementfound to be most useful with respect to the development of theseparticular wheels.

The stationary milling wheel is generally illustrated at 10. Theadjacent rotatable milling wheel is indicated at 30. The two wheels 10,30 are mounted along a common central axis shown at A-A. The stationarymilling wheel is fixed to a stationary shaft 1 supported on a frame 2. Acoaxial rotatable shaft 3 mounts the rotatable milling wheel 30. Eachwheel is mounted to its respective shaft by an outer collar 4 havinginterfitting projections 5 received within apertures in the wheels. Themilling wheels are secured to the respective shafts by removablethreaded nuts shown at 6. Material to be milled is fed through thestationary milling wheel from a hopper generally shown at 7 and exitsfrom frame 2 downwardly beneath the two wheels after being milled.

In this type of mill, the shaft 3 is powered by an electric motor (notshown). Provision is made for axial adjustment of shaft 1 relative toshaft 3 to provide adjustment of the clearance between the adjacentsurfaces on the milling wheels 10, 30. This permits the user to selectthe degree of fineness in the resulting flour.

This disclosure is concerned with the fabrication and details of themilling wheels, and not with the details of the mill itself. Otheralternative mechanical arrangements can be utilized for mounting thewheels for rotational movement of wheel 30 with respect to thestationary milling wheel 10.

As can be seen in the drawings, the two milling wheels have substantialareas of similarity, although they complement one another in actual use.They are preferably of the same diameter and thickness, although this isnot a necessary design factor. They are similarly mounted to the shafts1, 3, which simplifies the mounting process and allows for duplicationof the specific mounting elements. Again, this is not a determinativedesign factor.

The milling wheels 10, 30 illustrated in the drawings are preferablyfabricated from stoneware. A specific type of material found useful inthis product is "high fire-cone 10" stoneware. The wheels are moldedfrom green material and fired in the manner conventional to productionof stoneware items and pottery. After firing, the wheels are preferablyglazed about all of their exterior surfaces. The glazed surfaces aresubsequently fired in the conventional manner. As will be describedbelow, certain areas of the finished wheels are then machined forprecision accuracy and alignment purposes. The final surfaces on thewheel are therefore relatively smooth and hard.

Referring now to FIGS. 2 through 5, the stationary milling wheel 10presents a first radial surface 11 which faces inwardly in the matchedpair of wheels, and a second radial surface 12, which faces outwardly.The center of the second radial surface 12 is lightly machined at 13 toproduce a surface for engagement by collar 4 and to assure that thecollar 4 accurately mounts the wheel 10 along the central axis A--A.

The first radial surface 11 is interrupted at the center of wheel 10 bya center cavity 18. Cavity 18 is circular in shape and extends axiallyinward from the first radial surface 11. It is intersected by a radialaperture 19 leading from the upper periphery of the milling wheel 10.The upper end of aperture 19 is in open communication with the hopper 7for reception of granular material.

A stationary milling face is formed on the wheel 10 between the centercavity 18 and the outside milling wheel periphery 20. This annularmilling face is best illustrated in FIG. 3.

The annular milling face 14 is interrupted by a plurality of identicalgrooves 15 which are formed in communication with the center cavity 18.Each groove 15 extends radially outward to a location spaced inwardlyfrom the grinding wheel periphery 20. The annular area located outwardfrom the grooves 15 presents a rim 16 where final milling occurs. Rim 16is illustrated in FIG. 2 as being bounded by a dashed line 21. Thedashed line 21 does not physically occur on the milling wheel, but issimply a boundary for purposes of visually describing the operativeareas on the milling surfaces of the wheel 10.

The outer plane areas of the first radial surface 11 are interrupted bymultiple hemispherical recesses or dimples 17. These are indentations inthe otherwise flat surfaces. The recesses 17 diminish in diameter fromthe center of wheel 10 to its periphery 20. They extend between thegrooves 15 and about the rim 16. While only a portion of the surfacesare illustrated as being dimpled in the drawings, it is to be understoodthat this pattern is repeated about the complete face of each wheel.

The annular area about rim 16 is preferably machined. Because of thehardness of the fired clays used in stoneware, a diamond lap isparticularly suitable for this operation. The rim 16 is machined toremove the outer glazed surface, although a portion of the glazedmaterial still remains on the exposed stoneware, due to the porosity ofthe stoneware and resulting absorption of the liquid glaze duringfabrication of the wheel. For accuracy, the central area 13 at the outersurface 12 on wheel 10 is preferably machined on a lathe or othermachine tool about the same center as is the rim 16, insuring that boththe area 13 and the rim 16 are accurately formed across planesperpendicular to the central axis A--A. The removal of surface glaze canbe extended over all coplanar areas about surface 11.

The rotatable milling wheel 30 has a number of elements essentiallyidentical to those just described with respect to the stationary millingwheel 10. Obviously, the two wheels face in opposite directions, andsome of the elements are mirror images of one another. As can be seen inFIGS. 6 and 7 particularly, the rotatable milling wheel 30 includes afirst radial surface 31 and an outwardly facing second radial surface32. The surface 32 has a machined central area 33 to facilitate itsaccurate positioning by the abutting surface of collar 4. The inwardlyfacing or first radial surface 31 has a center cavity 38. A rotatablemilling face 34 extends annularly between the center cavity 38 and themilling wheel periphery 40. Grooves 35 lead outward from cavity 38 andextend to locations spaced inwardly from periphery 40. A machined rim 36is illustrated as being bounded by dashed line 41 and extends betweenthe line 41 and the milling wheel periphery 40. Hemispherical recessesor dimples 37 are arranged about the plane areas of the first radialsurface 31 and extend about the rim area outward from the ends of thegrooves 35. The rim 36 is machined in the same manner as discussed abovewith respect to rim 16.

The differences between the milling wheels 10, 30 relate to theirfunctions. The function of the stationary milling wheel 10 is to feedthe incoming annular material between the two wheels and to complementthe action of the rotatable surfaces on wheel 30 to assist in crackingand grinding the granular particles before final exit of the resultingflour from between the adjacent rims 16, 36 about the milling faces 14,34.

To accomplish efficient cracking of granular materials across themilling face 14 of the stationary wheel 10, there are provided aplurality of equiangularly spaced grooves 15 centered about the axisA--A. These grooves are seen in detail in FIGS. 2, 3 and 4.

Each groove 15 is defined by side walls 22 and 23, which aresubstantially perpendicular to the plane of the surface 12. They leadinwardly to a stepped bottom groove surface having lands 24a and 24beach substantially parallel to the plane of surface 11. The depth of theinner land 24a is one-half to three-quarters of the diameter of thelargest grains to be milled, while the depth to the outer land 24b isone-half to three-quarters of the diameter of the smallest grains to bemilled. This assures that at least one-quarter of each kernel willproject outward beyond the groove 15 for initial cracking. As anexample, the depth of land 24a might be 0.125 inches for soybeans orcorn, while the depth at land 24b might be 0.0625 inches for wheat.

In FIG. 3, the direction in which grain is dragged is illustrated by thearrow 25. This is the direction of rotation of the adjacent surfaces onthe rotatable milling wheel 30. The side wall 23 is therefore thedownstream wall or cutting side in each groove 15, against which grainis directed by rotation of the milling wheel 30. The side wall 22 istherefore the upstream surface.

The side wall 22 is offset slightly to the side of a radian through axisA--A in the direction of arrow 25. This angular deviation allowsmaterial to be dragged along grooves 15 as a result of the draggingforces applied to it by partial contact against the moving surfaces ofwheel 30. Wall 22 preferably defines an angle of about ten degrees withrespect to a radial line through the center of wheel 10. The walls 22,23 of grooves 15 diverge outwardly from the center of wheel 10, theangle of divergence being approximately five degrees. This divergency orflaring of grooves 15 resists the tendency of material within thegrooves to dam or pack within them, assuring room for continuousmaterial migration in a radial direction.

The individual grooves 15 terminate in enlarged cavities 27 open to thesurface 11. The inner surfaces of cavity 27 are tapered toward the planeof the surface 11 in both the radial direction and in the direction ofarrow 25. Therefore, grain particles within grooves 15 are forced towardthe adjacent rotating surfaces on wheel 30 by both centrifugal force andby the dragging frictional forces which lead them in the direction ofarrow 25.

While grooves 15 are designed to facilitate outward migration ofgranular particles, it has been found desirable to also provide means toimpede such motion temporarily in order that hard particles are notsimply wedged between the shearing walls of the wheels and moved outwardwith no resistance. This is accomplished by the ledge formed at the baseof each groove 15 between lands 24a and 24b, and by tangential teeth 23aformed along each groove wall 23. The teeth act as serrations to holdgrain while it is being sheared or cracked.

The details of grooves 35 on the rotatable milling wheel 30 areillustrated in FIGS. 7 and 8. Grooves 35 are formed in a teardrop shape,having curved walls progressively enlarged in width in a directionleading outward from the center cavity 38. They are curved tangentiallyin a direction opposite to the rotational direction of wheel 30, theintended direction of rotation being shown in FIG. 6 by the arrow 42.The walls of grooves 35 curve inwardly to corner edges formed at theirintersection with the first radial surface 31.

The rotatable milling wheel 30 is also illustrated as having radiallyinclined slots 43 which are stepped along their length and interrupt thesurface 11 and which terminate at the rim 36. The slots 43 are inclinedoppositely to the grooves 15, so that the respective indentations andrelatively straight side walls thereof tend to crack kernels of grainwith a "scissors" effect for more efficient shearing. They also haveteeth 43a along their cutting sides, to complement teeth 23a describedabove.

The teardrop-shaped grooves 35 serve a primary purpose of feedingsubstantial quantities of grain in a tangential direction outward fromthe center cavities 18, 38. The pressure of the incoming grain forcesthe material into the stationary grooves 15 of wheel 10 where thekernels are sheared by subsequent impact and grinding due to theindentations on the rotatable wheel surface 31. It is to be noted thatboth the grooves 15 and the grooves 35 expand in width in a directionradially outward from the axis at the center of the wheels 10, 30. Thisassures that there will be sufficient room to permit incoming materialto continuously be moved outwardly under the pressure of the feedinggranular material, eliminating the possibility of the partially crackedor milled material being jammed between constricting surfaces on thewheels.

The illustrated wheels accomplish milling by a combination of variouseffects. Primary reduction of the particles is accomplished by shearingor cracking the original kernels between the walls of the grooves 15, 35and the overlapping slots 43, which are formed in the rotatable wheel30. The hemispherical dimples or recesses 17 provide a multiple numberof small indentations which again overlap one another on the two wheelsand break the particles down into smaller sizes. Because of theirhemispherical shape, the recesses or dimples 17 produce a reduction inevery direction of movement of the particles between the two wheels 10,30. In contrast, the grooves 15, 35 and slots 43 cooperate to move andreduce the granular materials in a directional process which is bothradial and tangential. The grooves 15, 35 and slots 43 crack thekernels, while the dimples or recesses 17 reduce the particles to asmaller powder. Finally, the particles are ground between the abrasivesurfaces of the adjacent rims 16, 36, resulting in production of veryfine flours in a single pass of material through the area between thetwo wheels 10, 30. Because of the accurately machined rims 16, 36, andthe ability of stoneware to withstand rubbing movement, rims 16, 36 canactually be powered while lightly rubbing one another, thereby assuringthat the flour particles leaving from between them are in an extremelyfine ground state. It has been found practical to actually produce "cakeflour" from wheat by use of a home mill using these wheels. Similar fineflours can also be produced from other granular materials, includingboth soybeans and corn.

The described wheels have been designed and used on home mills poweredby three-quarter horsepower electric motors and driven at 1800 RPM. Thewheels tested in this manner had an outside diameter of five inches.They were capable of milling wheat at a rate of one pound per minute ata very fine setting with the rims 16, 36 lightly rubbing one another.The same milling capacity was found with respect to corn. They workedequally well in milling soybeans, a product which is impractical to millby use of abrasive milling wheels found commonly in home grain mills.The same wheels were found to be equally effective when powered at lowerspeeds, including half speed at 900 RPM.

Variations are possible with respect to the details discussed above, andfor these reasons only the following claims are intended as definitionsof my invention.

Having described my invention, I claim:
 1. In a matched pair of coaxialmilling wheels for small flour mills having a stationary milling wheeladapted to be fixed relative to a transverse axis and a coaxialrotatable milling wheel adapted to be powered about the transverseaxis:said milling wheels each having: (a) a circular disk having acentral axis; (b) first and second axially spaced radial surfaces formedon the disk and being joined by a peripheral surface; (c) a centercavity open to the first radial surface on the disk and extendingaxially inward therefrom a portion of the axial distance between thefirst and second radial surfaces; (d) a planar annular milling faceformed on said first radial surface between the center cavity and themilling wheel periphery; said stationary milling wheel furthercomprising: (a) a feed aperture formed within the milling wheel andleading from its peripheral surface to said cavity for directing graininward to the cavity for milling purposes; (b) said annular milling facehaving a plurality of grooves having side walls slightly offset from aradian through central axis and substantially perpendicular to the planeof said milling face, said grooves being angularly spaced about thecentral axis and extending from the center cavity to locations spacedinwardly from the milling wheel periphery of the stationary millingwheel; (c) each of said grooves increasing in width and decreasing indepth in a direction outward from the center cavity; (d) said stationarymilling wheel being fabricated as an inegral unit from fired stoneware,the exterior surfaces of the stationary milling wheel being glazed andfired during fabrication, and the outermost rim of the annular millingface between its grooves and wheel periphery having fired stonewarematerial exposed across a plane perpendicular to the central axis; saidrotatable milling wheel further comprising: (a) said annular millingface having a plurality of tangentially curved grooves each formed in ateardrop shape, having curved walls progressively enlarged in width in adirection leading outward from the center cavity, each groove being inopen communication with the center cavity of the rotatable millingwheel, said grooves being angularly spaced about the center axis andextending tangentially outward in a direction opposite to the intendeddirection of rotation of the rotatable milling wheel about the centeraxis, each groove extending from the center cavity to a location spacedinwardly from the periphery thereof; (b) each of said grooves increasingin width and decreasing in depth in a direction outward from the centercavity; (c) said rotatable milling wheel being fabricated as an integralunit from fired stoneware, the exterior surfaces of the rotatablemilling wheel being glazed and fired during fabrication and theoutermost rim of the annular milling face between the grooves and wheelperiphery having fired stoneware material exposed across a planeperpendicular to the central axis.
 2. An apparatus as set out in claim 1wherein the annular grinding faces of both milling wheels have aplurality of hemispherical recesses formed therein.
 3. An apparatus asset out in claim 1 wherein the annular grinding faces of both millingwheels have a plurality of hemispherical recesses formed therein andwherein the depth of the recesses progressively diminished toward thewheel periphery.
 4. A stationary milling wheel comprising:(a) a circulardisk having a central axis; (b) first and second axially spaced radialsurfaces formed on the disk and being joined by a peripheral surface;(c) a center cavity open to the first radial surface on the disk andextending axially inward therefrom a portion of the axial distancebetween the first and second radial surfaces; (d) a feed aperture formedwithin the milling wheel and leading from its peripheral surface to saidcavity for directing grain inward to the cavity for milling purposes;(e) a planar annular milling face formed on said first radial surfacebetween the center cavity and the milling wheel periphery; (f) saidannular milling face having a plurality of grooves having side wallsslightly offset from the radian through said central axis andsubstantially perpendicular to the plane of said milling face, saidgrooves being angularly spaced about the central axis and extending fromthe center cavity to locations spaced inwardly from the milling wheelperiphery; (g) each of said grooves increasing in width and decreasingin depth in a direction outward from the center cavity; (h) said millingwheel being fabricated as an integral unit from fired stoneware, theexterior surfaces of the milling wheel being glazed and fired duringfabrication, and the outermost rim of the annular milling face betweenthe grooves and wheel periphery having fired stoneware material exposedacross a plane perpendicular to the central axis.
 5. An apparatus as setout in claim 4 wherein the annular grinding face has a plurality ofhemispherical recesses formed therein.
 6. An apparatus as set out inclaim 4 wherein the annular grinding face has a plurality ofhemispherical recesses formed therein and wherein the depth of therecesses progressively diminishes toward the wheel periphery.
 7. Arotatable milling wheel comprising:(a) a circular disk having a centralaxis; (b) first and second axially spaced radial surfaces formed on thedisk and being joined by a peripheral surface; (c) a center cavity opento the first radial surface on the disk and extending axially inwardtherefrom a portion of the axial distance between the first and secondradial surfaces; (d) an annular milling face formed on said first radialsurface between the center cavity and the milling wheel periphery; (e)said milling face having a plurality of tangentially curved groovesformed in a teardrop shape, each groove having curved wallsprogressively enlarged in width in a direction leading outward from thecenter cavity, said grooves being angularly spaced about the center axisand extending tangentially outward in a direction opposite to theintended direction of rotation of the milling wheel about the centeraxis, each groove extending from the center cavity to a location spacedinwardly from the milling wheel periphery; (f) each of said groovesincreasing in width and decreasing in depth in a direction outward fromthe center cavity; (g) said milling wheel being fabricated as anintegral unit from fired stoneware, the exterior surfaces of the millingwheel being glazed and fired during fabrication, and the outermost rimof the annular milling face between the grooves and wheel peripheryhaving fired stoneware material exposed across a plane perpendicular tothe central axis.
 8. An apparatus as set out in claim 7 wherein theannular grinding face has a plurality of hemispherical recesses formedtherein.
 9. An apparatus as set out in claim 7 wherein the annulargrinding face has a plurality of hemispherical recesses formed thereinand wherein the depth of the recesses progressively diminishes towardthe wheel periphery.